PowerShell: Replace underscores with either a period or @ sign

In PowerShell, I'm looking to convert a SharePoint Location string (john_smith_domain_com) to the proper addressing of john.Smith@domain.com.
I'm not sure which is the best way to go about doing this.
I know $var.Replace("_",".") would work to replace all the "_"s with "."s, but that doesn't help the "@" going between the name and the domain.

Unfortunately, the domain isn't always the same, or I'd be able to just .replace it easily.

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You can combine two -replace operations (this assumes a two-component domain name, such as domain.com):

# -> 'john.smith@domain.com'
'john_smith_domain_com' -replace '_(?![^_]+_[^_]+$)', '.' -replace '_', '@'

• Regex _(?![^_]+_[^_]+$) matches all _ chars. except the second-to-last one.

  • For an explanation of the regex and the ability to interact with it, see this regex101.com page.

• After all these have been replaced with ., only the second-to-last one is left, which can then be replaced with @

As JohnLBevan notes, if there are domain names with a varying number of components, you have two options:

• If you can assume that all users names are in the form <firstName>.<lastName> (as governed by a policy), you can replace the second _ with @:

# -> 'john.smith@domain.co.uk'
'john_smith_domain_co_uk' -replace '^([^_]+)_([^_]+)_', '$1.$2@' -replace '_', '.'

• Otherwise, as John notes:

> You may want something that's aware of the more common TLDs / caters for more common domain formats. Some options are in this post.